Independent personal services: residence taxation unless fixed base or presence exceeding threshold gives source state taxing right. Resident state taxation is primary for income from professional or other independent activities unless the individual has a fixed base in the other Contracting State or remains in that State beyond the treaty's presence threshold; if either connection exists, the other State may tax only the income attributable to that fixed base or derived during the period of presence. 'Professional services' includes independent scientific, literary, artistic, educational or teaching activities and specified independent occupations such as physicians, lawyers, engineers, architects, dentists and accountants.